Conservative leadership hopeful Sir Malcolm Rifkind has admitted he has "a problem" with people thinking he is much older than his actual 59 years.
Sir Malcolm was foreign secretary in the 1990s.
The ex-foreign secretary said he was the same generation as David Davis, 56, and was full of "vitality and energy".
"A lot of people think that because I was a colleague of Ken Clarke(65) and Michael Howard(64) that I am the same age - I'm not," he told ITN.
The misconception came because he was made a senior minister at a young age.
Sir Malcolm was replying to comments put to him from ex- Daily Telegraph editor Max Hastings that he was "too old" to be the new Tory leader.
"I have still got an enormous amount of vitality and energy as Max Hastings and others will find out," Mr Rifkind told interviewer Alastair Stewart.
Michael Howard has said he believes he is too old to lead the Tories into the next election, while some commentators have questioned whether Mr Clarke is too old to take on the role.
"They are in their mid sixties, I am the same age as David Davis, we are the same generation," said Sir Malcolm, who is shadow work and pensions secretary.
Stressing that he would not make any "vainglorious boast" of winning the leadership, Sir Malcolm said the party should choose "a strategy" before choosing a leader.
"If the party should choose the strategy of One Nation Conservatism, then I should be proud to lead the Conservative Party," he added.
He said the party was in a stronger position than two years ago, but that the improvement in their position was still "painfully slow".
By returning to its One Nation traditions the party would appeal to the "wider public".
Potential other candidates expected to compete for Mr Howard's job include: Liam Fox, Theresa May, David Cameron, Andrew Lansley, David Willetts, Tim Yeo and David Davis, who is the bookmakers' favourite.